In case of a mass spectrometry, sample molecules are ionized and introduced into a vacuum chamber or ionized in the vacuum chamber, then the ion movement in an electromagnetic field is measured, thereby measuring the mass charge ratio m/z (m: mass, z: the number of charges) of the object molecular ions. In this case, because what is obtained is a mass-to-charge ratio (m/z), it is difficult to obtain the internal structure information of the object molecular ions, as well. This is why a so-called tandem mass spectrometry is often used. This tandem mass spectrometry carries out the first mass spectrometric operation to identify or select sample molecular ions. These ions are referred to as precursor ions. Then, the tandem mass spectrometry carries out the second mass spectrometric operation to dissociate those precursor ions with use of a method. The dissociated ions are referred to as fragment ions. These fragment ions are further subjected to a mass spectrometric process to obtain a fragment ions generation pattern. The use of this dissociation pattern makes it possible to estimate the arrangement structure of the precursor ions. The tandem mass spectrometry is widely employed for such mass spectrometers as the ion trap, ion trap time-of-flight, triple quadrupole, and quadrupole time-of-flight ones. Particularly, the ion trap and ion trap time-of-flight spectrometers can carry out plural tandem mass spectrometric operations, thereby enabling efficient structure analysis of ions.
There is still another quadrupole ion trap mass spectrometer employable for mass spectrometry capable of tandem mass analysis. As such a quadrupole ion trap, there are Paul trap consisting of a ring electrode and a pair of end cap electrodes, and a quadrupole linear ion trap consisting of 4 cylindrical electrodes. If a radio frequency voltage of 1 MHz or so is applied to a ring electrode or cylindrical electrode, ions that are over a certain mass level come to be stabilized in a quadrupole ion trap, thereby ions can be accumulated therein.
Each of the triple quadrupole and quadrupole time-of-flight mass spectrometers is provided with a quadrupole mass filter in the preceding stage of its ion dissociation device. The quadrupole mass filter passes only ions having a specific mass-to-charge ratio (m/z) and excludes other ions. The quadrupole mass filter can also scan the mass-to-charge ratio (m/z) of the passing ions, thereby identifying and selecting object ions.
U.S. Pat. No. 5,847,386 discloses a method of how to shorten the ejection time of ions in a triple quadrupole mass spectrometer and a quadrupole time-of-flight mass spectrometer respectively. According to the method, a multipole rod electrode disposed in an ion dissociation device is inclined or an inclined electrode is inserted between multipole rod electrodes to generate a DC electric field on the center axis of the multipole electrode in the exit direction, thereby shortening the ejection time of ions.
JP-A-2005-044594 describes a collisional-damping chamber formed by introducing such an He gas, etc. into a quadrupole electrode so as to connect an ion trap to a time-of-flight mass spectrometer. This spectrometer enables ion measurements in a wider dynamic range of mass-to-charge ratio (m/z), thereby realizing tandem mass analysis at high sensitivity and at high precision.